Thermally responsive switch structures



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June 17, 1958 H. D. EPSTEIN THERMALLY RESPONSIVE SWITCH STRUCTURES Filed March 28, 1957 4 Sheets-Sheet 4 MN MWN United States Patent THERMALLY RESPONSIV E SWITCH STRUCTURES Henry David Epstein, Boston, Mass., assignor to Metals & Controls Corporation, Attleboro, Mass, a corporation of Massachusetts Application March 28, 1957, Serial No. 649,206

4 Claims. (Cl. 200-138) This invention relates to a novel thermally responsive, snap-acting member and to a novel, thermally responsive, mechanically resettable, trip-free, electrical switch in-' corporating such a member.

One of the objects of this invention is to provide such a member and/0r such a switch which will be capable of being easily and accurately calibrated for trip-free operation.

A further object of this invention is to provide such a member and/or such a switch whereby less force is required to be exerted to reset said member from one condition to another.

A further object of this invention is to provide such a member and/0r such a switch whereby the design thereof for a particular installation is simplified.

A further object of this invention is to provide such a member and/ or such a switch which is capable of lower current ratings and more rapid tripping time intervals.

A further object of this invention is to provide such a member and/ or such a switch which is economical to manufacture and dependable in use.

Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the means, elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and

the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are i1- lustrated:

Fig. l is a side view of a thermally responsive, snapacting member according to a first embodiment of this invention;

Fig. 2 is a bottom plan view thereof;

Fig; 3" is a top plan view, on a scale reduced from that of Figs. 1 and 2, of a circuit breaker according to said first embodiment;

Fig. 4 is a view similar to Fig. 3 but with certain of the parts, including the cover plate and reset button, removed;

Fig. 5 is a sectional view taken along lines 5-5 of Fig. 3 but on the same scale as that of Figs. 1 and 2;

Fig. 6 is a view similar to Fig. 5 but partly in phantom and showing the push-button in fully depressed position and the snap-acting member in its downwardly bowed condition;

Fig. 7 is a sectional view taken along lines 7-7 in Fig. 6';

Fig; 8 is a side view of a thermally responsive, snapac'ting member according to a second embodiment of the invention;

Fig. 9 is a bottom plan view thereof;

Fig, 1( is a top plan view, on a scale reduced from that of Figs.- 8 and 9", of a circuit breaker according to the second embodiment of the invention;

K 2,839,638 Patented June 17, 1958 Fig. 11 is a sectional view taken along line 11-11 in Fig. 10 and on the same scale as that of Figs. 8 and 9;

Fig. 12 is a view similar to Fig. 11 but showing the reset button in its fully depressed position and the snapacting member in its downwardly bowed condition; and

Fig. 13' is a sectional view taken along line 13-13 in Fig. 12.

Referring to Figs. 1-7, a first embodiment of this invention is shown. According to this imbodiment, athermally responsive, electrical switch is provided which is generally indicated by the numeral 20 and which takes the form of a mechanically resettable, trip-free circuit breaker. Circuit breaker 20 includes a base 22 formed of one of the customary molded plastics and fixedlymounting an internally threaded bushing 24. A supporting post 26 is adjustably mounted in threaded engagement with bushing 24. After adjustment along bushing 24, post 26 may be retained in adjusted position by depositing a cementitious compound at 27 as shown in Figs. 5-7. Fixedly carried by supporting post 26 are a pair. of flange-providing members 28 and 30, respectively, and a sleeve 32.

The novel, thermally responsive, snap-acting member of. this invention includes a thermally responsive, snapacting element 34 which is mounted between the flanges provided by members 28 and 30 in the manner now to be described. Snap-acting element 34 is provided with an aperture 36 within which are disposed a cylindrical, reduced-diameter portion of member 28 and a portionof supporting post 26. Snap-acting element 34 is loosely confined between the flanges provided by members 28 and 30 againstv substantial movement longitudinally of the post. Since snap-acting element 34 is loosely confinexl between the flanges provided by members 28 and 30, the snap-acting element would be substantially free to rotate about the supporting post unless otherwise confined thereagainst. It will be obvious that snap-acting element 34 is assembled with members 28 and 30 on post 26 before the assembly of. sleeve 32 with the post and the subsequent securing together of members 28, 36 and 32 on the post. The adjacent end of post 26 is headed. over at 38 against afiange 40 carried by sleeve 32 as best shown in Fig. 5, so to secure these members on the post.

Snap-acting element 34 is thermally responsive, being formed of two materials having mutually difierent coefiicients of expansion. as described, for example, in US. Patent No. 1,448,240 granted on March 13, 1923, to I. A. Spencer. Element 34 carries a pair of contacts 42 and 44, respectively, in electrical connection therewith. Preferably but not necessarily, contacts 42 and 44 are secured to element 34 through. the intermediary of members or plates 46 and 48, respectively, in the manner and for the purposes described in my copending application Serial No. 497,109, filed. March 28, 1955. It is to be noted that element. 34 carries contacts 42 and 44 in mutually spaced, diametrically opposed relation to each other.

According to the present. invention, the thermally responsive, snap-acting member includes a pair of extensions or cars 50 and 52, respectively, which are carried by snap-acting element 34 in mutually spaced, diametrically opposed relation to each other. Each of extensions 50 and 52 extends from its junction with snap-acting element 34 away from the other and in a direction substantially perpendicular to a straight line joining contacts 42 and 44. Although ears 50 and 52 could be separately formed (of thermally responsive or nonthermally responsive material) and subsequently secured to the snap-acting element, the snap-acting member (exclusive of contacts 42 and 44 and bars 46 and 48) is preferably formed with integral cars 50 and 52' all as a 3 one-piece blank from a unitary piece of thermally responsive material.

Snap-acting element 34 is automatically snappable, in response to temperature change in one direction (upon heating thereof due, for example, to the flow of a current overload therethrough), from the first position or downwardly bowed condition as shown in Figs. 6 and 7 and in broken lines in Fig. to a second position or upwardly- -bowed condition as shown in full lines in Fig. 5. As

shown in Fig. 7, when element 34 is in said first position contacts 42 and 44 are in electrically conductive engagement with contacts 54 and 56, respectively. Contacts 54 and 56 are provided at one end of terminal members '58 and 60, respectively, the latter being disposed in tightened threaded engagement with bushings 62 and 64, respectively, which are fixedly carried by base member 22. It will be apparent that by rotating post 26 relative to bushing 24, the pressure exerted by contacts 42 and 44 against contacts 54 and 56, respectively, can be adjusted. Itwill further be noted that contacts 42 and 44 -are maintained in alignment with contacts 54 and 56,

respectively, and element 34 and resetting member 70 are maintained against substantial rotation about post 26, all byany suitable means such as recesses 66 and 68 provided by casing 22 and within which lie the adjacent portions of the resetting member and the-outermost portions ofextensionsSil and 52, respectively. It will be seen that when element 34 is in the said first position as shown in Fig.7, contact 42 engages contact 54, contact 44 engages contact 56, and element 34 electrically connects contacts 54 and 56. Also, when snap-acting element 34 is in the said second position as shown in full lines in Fig. 5, contacts 42 and 44 are separated from contacts 54 and 56, and contacts 54 and 56 are electrically disconnected from each other. Preferably, the characteristics ofsnap-acting element 34 are such that, under normal temperature conditions, it is incapable of automatically snapping from said second condition back to said first condition in response to temperature changes in the opposite direction. By normal temperature conditions are meant such conditions as it is expected that the device will normally encounter.

In order to snap snap-acting element 34 from said second condition as shown in full lines in Fig. 5 to said first condition as shown in Figs. 6 and 7, manual resetting means is provided. In this regard, a resetting plate or member 70 is provided which is fixedly secured to a collar '72. Collar 72 is freely slidable on sleeve 32 between limits fixed by engagement of the collar with flange 40 carried by sleeve 32 and with the flange provided by member 30. It will be apparent that collar 72 must be assembled on sleeve 32 before supporting post 26 is headed over at 33. A push-button 74 is secured to collar 72 in any convenient manner such as by force-fitting collar 72 within the socket 75 provided by the push-button. A compression spring 76 having one end biased against the push-button and having its other end biased against the headed portion 38 of supporting post 26, resiliently biases the push-button and resetting plate 70 upwardly to the position as viewed in Fig. 5. By depressing or advancing push-button 74 from the position of Fig. 5 to that of Figs. 6 and 7, resetting member 70 is correspondingly advanced to move the relatively adjacent portions of member 70 against extensions 50 and 52 whereby the snap-acting element may be snapped from the upwardly bowed condition shown in Fig. 5 to the downwardly bowed condition shown in Figs. 6 and 7.

Circuit breaker 20 is adjusted to provide trip-free operation as described, for example, in U. S. Patent No. 2,199,388 granted on May 7, 1940, to J. D. Bolesky. By trip-free operation it is meant that snap-acting element 34 will be fi'ee to snap automatically from said first condition as shown in Figs. 6 and 7 toward said second condition as shown in full lines in Fig. 5 sufiiciently electrically to disconnect contacts 42 and 44 from contacts 54 and 56 upon temperature change in the above-mentioned one direction regardless of the position or actuation of the resetting means. Referring to Figs. 6 and 7, push-button 74 and resetting member 70 are in their fully depressed position and, as best shown in Fig. 6, snap-acting element 34 is free to snap toward said second condition electrically to disconnect contacts 42 and 44 from contacts 54 and 56, respectively, even though the push-button and resetting means are retained in said fully depressed positions. It follows that since the device is trip-free, full depression of the push-button and resetting means will not be effective to snap the snap-acting element from said second condition to said first condition when the latter is above the maximum resetting temperature.

In order that the device be trip-free as explained above, the extent of depression or advancement of the portions of resetting member 7% that engage extensions 50 and 52 is so adjusted that the resetting member will snap the snap-acting element from the full-line to the broken-line position shown in Fig. 5 before push-button 74 and resetting member 70 have been fully depressed but will not prevent snapping of the snap-acting element from the broken-line toward the full-line position of Fig. 5 sufficiently to disconnect contacts 42 and 44 electrically from contacts 54 and 56. This adjustment is ordinarily effected by bending resetting member 70 to adjust the vertical height of the end portions thereof as viewed in Fig. 5 and, due to the vagaries of spring-back and other problems, it is diflicult to obtain this adjustment accurately and quickly. This gives rise to a number of the advantages of this invention for the reason that the provision of extensions or cars 50 and 52 results in a greater eifective width of the snap-acting means for manually resetting purposes. For example, with an increased effective width of the snap-acting means for resetting purposes, the tolerance of the range of adjustment of resetting member 70 is increased, the ease and accuracy of calibration are improved, the throw of the resetting means is increased,

and the force required to be exerted to reset the snapacting means is decreased.

The provision of extensions 50 and 52 has substantially no efiect on the electrical characteristics of the snapacting element, and this increase in the effective width of the snap-acting element for resetting purposes is not accompanied by a corresponding decrease in the electrical resistance of the element. In this regard, whether or not members 46 and 48 are utilized, practically none of the current flowing through the snap-acting element flows through either of the extensions. It will be apparent then that the snap-acting element of this invention has an efiective width (in a direction perpendicular to a straight line joining the contacts) for manual resetting purposes equal to the distance from the outer edge of one of the extensions to the outer edge of the other extension, and, with respect to its electrical characteristics, ordinarily has a corresponding width equal to the distance between the junctions of the extensions 50 and 52 with the snapacting element.

The otherwise open end of base or casing 22 may be closed by seating a gasket 78 and cover plate 80 as shown in Figs. 5 and 7, and securing this gasket and cover plate in place by means such as bolts (not shown) having their shanks disposed in holes 82 and 84, respectively, and retained by nuts (not shown).

Referring to Figs. 8-13, a thermally responsive, mechanically resettable, trip-free circuit breaker is shown which forms a second embodiment of this invention. This circuit breaker is generally indicated by the numeral and includes a base or casing member 92 formed of one of the customary molded plastics. Three terminals 94, 96 and 98 are fixedly secured to base 92 in any suitable manner such as by molding the base about these terminals. Each of the terminals is formed of electrically conductive material, and terminals 94 and 98 are provided with overturned portions 100 and 102, respectively, to form electrical contacts. An auxiliary heater 104 is electrically connected at one end to an overturned portion 106 of terminal 96 and at the other end to contact 102. Auxiliary heater 104 is a resistance element and is disposed in heattransfer relation with the snap-acting element 108 of this embodiment.

Snap-acting element 108 is formed of composite, thermally responsive material in the manner described with respect to the snap-acting element of the previously described embodiment. Element 108 includes a mounting aperture 110 disposed substantially centrally thereof. A pair of contacts 112 and 114 are electrically connected to snap-acting element 108 and may be mounted thereon through the intermediary or bars or strips 116 and 118 in a manner similar to that described with respect to the previously described embodiment. The novel snap-acting member of this embodiment includes a pair of cars or extensions 120 and 122 carried by snap-acting element 108, each of which ears or extensions extends from its junction with element 108 away from the other and in a fixed relation with the base by means such as a lock nut 132.

Resetting means, along with snap-acting element 108, are mounted on supporting post 128 in a manner now to be described. The resetting means includes a resetting member 134 fixedly secured to a collar 136. Collar 136 is fixedly secured to a push-button 138 in any suitable manner such, for example, as by force-fitting collar 136 into a socket 140 provided by the push-button.

Supporting post 128 of this embodiment includes a flange 142, a' reduced-diameter cylindrical portion 143, and a cylindrical shank 144 of a diameter smaller than that of portion 143. In assembling the resetting means and the snap-acting means on supporting post 128, snapacting element 108 is disposed with portion 143 of the post within aperture 110, a flange-providing member 145 and a sleeve 146 (with collar 136 thereabout) are placed on shank 144, after which supporting post 128 is headed over at 148 against a flange 147 carried by sleeve 146. In this manner, snap-acting element 108 is confined against substantial movement along post 128 but would be rotat able thereabout unless otherwise confined against such rotation. Subsequently, a compression spring 149 is placed in socket 140 of the push-button and the forcefitting of collar 136 into socket 140 of push-button 138 is carried out. It will be apparent that spring 1 49 resiliently biases resetting member 134, collar 136 and pushbutton 130 upwardly as viewed in Figs. lll3 and in a direction away from snap-acting element 108.

Either one or" previously described recesses 124 and 126, and either one of recesses 152 and 154 which are provided by resetting member 134 may be disposed in registry with a ridge 150 provided by base 92. In this regard and as shown in the exemplary construction of Figs. -13, recesses 12d and 152 are in registry with ridge 150 whereby resetting member 134 and snap-acting element 108 are maintained in alignment with each other and against substantial rotation relative to base or casing 92.

Resetting member 134 may be provided with projections 156 and 158 which, when push-button 138 is depressed or advanced from the position shown in Fig. 11 to that shown in Figs. 12 and 13, are moved against ears 120 and 122, respectively, to snap the snap-acting element from the upwardly bowed condition shown in Fig. 11 to the downwardly bowed condition shown in Figs. 12 and 13.

Circuit breaker having been adjusted to provide tripfree operation as described above with respect to the previously described embodiment, the snap-acting element must, of course, be at or below the maximum resetting temperature in order that the element be reset by depres sion of the push-button as described above. In the manner described above with respect to the embodiment of Figs. l-7, the throw of the resetting means of the embodimentof Figs. 8-13 is determined at one end thereof by the engagement of collar 136 with a flange 147 on sleeve 146 and at the other end thereof by the engagement of resetting member 134 with flange-providing member 145.

When snap-acting element 108 is in the downwardly bowed position or condition shown in Figs. 12 and 13, contact 112 is in engagement with contact 102, contact 114 is in engagement with contact 100, the snap-acting element electrically connects contacts and 102 and auxiliary heater 104 is electrically connected in series circuit relation with the snap-acting element. With snap-acting element 108 in the upwardly bowed position or condition as shown in Fig. 11, contacts 100 and 102 are electrically di connected from each other and from contacts 114 and 112, respectively, and auxiliary heater 104 is electrically disconnected from snap-acting element 108. As with the embodiment of Figs. 1-7, snap-acting element 108 is preferably incapable, under normal temperature conditions, of automatically snapping from said second condition to said first condition in response to temperature change.

The circuit breaker of this embodiment is trip-free in the same manner as that described above with respect to the previously described embodiment. When it is realized that, ordinarily, the tolerance of the adjustment of the resetting means of this type of device to render it trip-free is often measured in terms of thousandths of an inch, the value of this invention becomes more apparent. In this regard, this invention provides the advantage of increasing this tolerance and the device is thereby rendered trip-free more readily. This is the case since depression of push-button 138 and resetting member 134 a given amount will deflect a given point on the snapacting element a lesser amount than corresponding depression of the push-button and resetting member of a conventional device. The increase in this tolerance, of course, leads to greater accuracy of calibration of the device.

Another advantage flowing from the present invention is that the force required to reset the snap-acting element is greatly reduced. It will be clear that the snap-acting member of this invention has an effective width (in a direction perpendicular to a line joining the contacts carried thereby) for manual reset purposes equal to the distance from the outer edge of one of the ears to the outer edge of the other ear, and has an effective width with respect to its electrical characteristics equal to the distance between the respective junctions of the ears with the snap-acting element. Accordingly, the snapacting member of this invention displays the characteristics of decreased resetting force in combination with decreased tripping time.

Recognizing that the design of a snap-acting member and/or an electrical switch of the above-descrdibed class requires the manipulation of a number of different variables (such as the electrical resistivity of the materials used, the cross-sectional area of the snap-acting element, etc.) to obtain the desired electrical, mechanical and thermal characteristics to be exhibited by the member and/or switch, it will be apparent that this manipulation of variables is greatly simplified with this invention since, among other reasons, the effective width of the member for resetting purposes can be determined substantially independently of the remaining variables and vice versa.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

'7 The dimensions of certain of the parts as they appear in the drawing have been adjusted for the purposes of clarity of illustration.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended thatjall matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A composite, thermally responsive, snap-acting element; said element being responsive to temperature change in one direction automatically to snap from a first condition to a second condition; said element carrying a pair of extensions and a pair of electrical contacts; said contacts lying in mutually spacer relation to each other; and said extensions extending from said element, away from each other, in mutually spaced relation to each other, and along a line substantially perpendicular to a line joining said contacts.

2. A composite, thermally responsive, snap-acting element; said element carrying a pair of electrical contacts and being responsive to temperature change in one direction automatically to snap from a first condition to a second. condition; said contacts being electrically connected to said element and disposed in mutually spaced, diametrically opposed relation to each other; a pair of extensions carried by said element; said extensions being disposed in mutually spaced, diametrically opposed relation to each other; and each of said extensions extending from said element in a direction substantially perpendicular to a line joining said contacts and in a direction away from the other extension.

3. A thermally responsive, mechanically resettable, trip-free, electrical switch comprising: a base; a pair of mutually spaced, electrical contacts supported by said base; a composite, thermally responsive, snap-acting element supported by said base; said snap-acting element being responsive to temperature change in one direction automatically to snap from a first condition to a second condition; said snap-acting element electrically connecting said contacts when in said first condition and being separated from and electrically disconnecting said contacts when in the other of said conditions; a pair of extensions carried by said element; each of said extensions being disposed in spaced, diametrically opposed relation to the other and extending from said snap-acting element in a direction away from the other; resetting means mounted adjacent said snap-acting element for movement relative to the latter; said resetting means being movable in. a first direction against both of said extensions to snap said snap-acting element from said second condition to said first condition; and stop means limiting the extent of advancement of said resetting means in said first direction thereby to permit snapping of said snap-acting element from said first condition toward said second condition when said resetting means is fully advanced in said first direction.

4. A thermally responsive, mechanically resettable, trip-free, electrical switch comprising: a base; a first pair of mutually spaced, electrical contacts; said first pair of contacts being supported by said base; a composite, thermally responsive, snap-acting element supported by said base; said snap-acting element carrying a second pair of contacts in mutually spaced, diametrically opposed relation to each other; each of the contacts of said second pair being electrically connected to said snap-acting element; said snap-acting element being responsive to temperature change in one direction automatically to snap from a first condition to a second condition; each of the contacts of said second pair being engaged with one of the contacts of said first pair when said snapacting element is in said first condition and the contacts of said second pair being separated from the contacts of said first pair when said snap-acting element is in said second condition; a pair of extensions carried by said element; each of said extensions being disposed in spaced, diametrically opposed relation to the other; each of said extensions extending from said snap-acting element in a direction substantially perpendicular to a straight line joining said contacts and in a direction away from the other extension; resetting means mounted adjacent said snap-acting element for movement relative to the latter;

References Cited in the file of this patent UNITED STATES PATENTS Bolesky et a1. Jan, 27, 1948 Mang Mar. 15, 1955 

